Investigation of Selected Geotechnical Properties of Excavated Subgrade Stabilized with Fly Ash for Reuse as Subbase

Abstract

Lateritic soil is among the most commonly used materials for road construction. However, constructing roads withpoor lateritic soil is one of the causes of road failures in Nigeria resulting in loss of lives and properties. Therefore, this study investigated fly ash as a stabilizing agent for excavated subgrade for reuse as subbase. Soil samples were obtained at depths of 1 m and distances of 10 m along Sango-Ota-Owode expressway at right hand and left hand sides of the road, while fly ash was purchased from Nigerian Building and Road Research Institute (NBRRI), Ota, Ogun State, Nigeria. Fly ash was characterized for its oxides in Central Research Laboratory, Bells University of Technology (BELLSTECH), Ota using the United States Environmental Protection Agency (2001) standards. Fly ash was added to excavated soil samples at 2%, 4% and 6% by dry weight of the soil respectively and selected geotechnical (particle size distribution, compaction, California bearing ratio and Atterberg’s limits) tests were conducted on both natural and stabilized lateritic soil samples in accordance with BS 812-102:1984, BS 812-103.1:1985 and BS 1377 part 2-4 (1990) standards. Fly ash results revealed significant amounts of SiO2, Al2O3, Fe2O3 and K2O, with other oxides present in trace amounts. Soil analyses revealed that as percentage addition of fly ash increased, there was corresponding improvement in analyzed geotechnical parameters of soil samples at both sides of the road, thereby confirming the efficacy of the fly ash. Results also revealed that the percentage addition of fly ash that produced the optimal stabilization value was 4%. This study concludes that fly ash is a good stabilizing agent for excavated subgrade to be reused as sub-base. This study recommends future reuse of fly ash in construction activities of related nature.